Hybrid vehicles refer generally to HEVs (Hybrid Electric Vehicles) which use two power sources, and the power sources are mainly an engine and an electric motor. In recent years, hybrid vehicles have been actively developed since they have an advantage of reducing emissions as well as having higher fuel efficiency and power performance, compared to vehicles having only internal combustion engines.
Such a hybrid vehicle may operate in either of two traveling modes according to which power train is driven. One is an EV (Electric Vehicle) mode, in which the vehicle is driven using only an electric motor, and the other is an HEV (Hybrid Electric Vehicle) mode, in which the vehicle is driven using power obtained by operating an engine together with the electric motor. The hybrid vehicle switches between the two modes while traveling depending on conditions.
Hybrid vehicles may be classified into various types depending on the arrangement of and connection between a motor and an engine. Among them, in a hybrid vehicle adopting a parallel-type or TMED-type (Transmission Mounted Electric Device type) hybrid system, an electric motor and an engine clutch (EC) are disposed between an engine and a transmission. The engine clutch serves to interconnect or disconnect the rotary shafts of the motor and the engine. Typically, interconnection is performed when the RPMs of the engine and the motor are close to each other within a certain range. Accordingly, it is necessary to know the RPMs of both the engine and the motor in order to control the engine clutch in the vehicle.
However, in a situation where it is difficult to known the RPM of the motor in the vehicle due to failure of the resolver of the motor or the like, it is impossible to perform the engagement control of the engine clutch. For this reason, the driving force of the engine may not be fully transmitted to a drive shaft, and hence starting performance may be deteriorated.